Houston, we have an issue with the SDR setup

19/11/2014 / ea3hoe / 0 Comments

So in general i am happy with my SDR setup. I cannot imagine going back to use my radio “in the blind” without being able to see what is happening on the band. Most of the stations i work are stations that haven’t been spotted on the cluster yet. SDR helps me to discover those stations and work them before the pile-up caused by the clusters starts.

I have spent my time mostly on 10m. I am very surprised that this band is so active the last months. I don’t know why that is. I was always under the impression that 20m was the most active band, but when i look at my bandscope i see much more stations on 10m than on 20m. And it’s not my antenna setup that is deaf on 20m because when i look at the cluster stats i also see roughly twice the amount of 10m spots compared to 20m spots. Anyway, band perculiarities set aside. Houston, we have a problem with the SDR setup.

As i mentioned in previous articles when i was building the SDR solution, i pick my IF signal from CN303 which is on the RX-2 path. Why? Because the IF sits on 73.095MHz which is a frequency i can “hear” with my RTL-SDR adapter. The IF on RX-1 sits on 11.374MHz and the RTL-SDR doesn’t go that low. Because i have almost solely been working on 10m i haven’t noticed anything wrong with my SDR setup. After all, everything between 21.5 and 30.0MHz goes through the RX-2 path.

Yesterday i wanted to work a few stations on 20m and i noticed that my SDR doesn’t receive anything unless i set my RX filter wider than 2700Hz, then suddenly CN303 gives me a signal again. In the image above you can see how it looks on the band scope. It’s either nothing (filter narrower than 2700Hz) or the normal bandscope as i am used to see (filter wider than 2700Hz).

In the Service Manual i found a table that shows which RX path is chosen when and as you can see in this table there are quite a few moments where i need to open the filter to be able to hear anything at all. Most significant (to me) are the 15m band and the 20m band. Below 20m there is nothing for me to do anyway because of antenna conditions.

Thinking about it it’s not a huge problem (so Houston, you can get back to work again), but merely an inconvenience. Now that i get used to the TS-590 i started to play with the RX filter and equalizer settings and i found that i get the most out of the radio with the filter set appx 1600-1800Hz wide (300-400 Low and 2000-2200 High) and the RX equalizer to one of the two High Boost settings (HB1 or HB2). Now i need to get used to use a much wider filter setting and change the RX equalizer setting for 14 and 21MHz if i want to continue to use the bandscope to help me find stations that were not spotted yet.

Reading it back, what does this article actually tell you? Not much, really. Many times i just start writing to get my thoughts and priorities straight and fixing this SDR “problem” is now, after writing this article, not a priority anymore.